Chemical Modification of Soy Proteins - ACS Publications

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C h e m i c a l M o d i f i c a t i o n of Soy Proteins

Downloaded by GEORGETOWN UNIV on November 1, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/ba-1977-0160.ch003

EDWIN W. MEYER and L. D. WILLIAMS Food Research, Central Soya Co., Inc., Chicago,Ill.60639

This selective review, which deals primarily with the chem cal modification of soy proteins, is further limited to non -destructive chemical reactions which alter physical and biochemical properties of importance in food systems. Soy protein products have been modified by various chemical reactions including: (a) treatment with alkalies and acids, (b) acylation, (c) alkylation and esterification, and (d) oxidation and reduction. In most instances these reactions have been applied to heterogeneous protein mixtures con taining nonprotein impurities, and often to proteins of unknown prior history. Nonetheless, these reactions indi cate that protein functional properties of value in food fabrication can be altered significantly through reaction with chemical reagents. It is recognized that chemically modified proteins must be critically evaluated for food safety. Touring the pastfifteenyears a number of soy protein products have become established as useful ingredients in the manufacture of processed foods. The growing acceptance of these products for use in food manufacture has been prompted by their varied functional prop erties and good nutritional qualities. Examination of current utilization patterns indicates that these protein products are used in food for the extension and replacement of traditional protein ingredients and as components in newly designed foods ( Table I ). The use of soy protein products is expected to continue to grow because of the increasing cost and decreasing availability of traditional animal protein foods and food ingredients, and the prospect of an inadequate supply of protein-calorierich foods on a worldwide basis. Much progress has been made in developing commercial soy protein products with differing functional characteristics. This has been accom52 Feeney and Whitaker; Food Proteins Advances in Chemistry; American Chemical Society: Washington, DC, 1977.

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Table I.

Modification of Soy Proteins

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Food Uses of Soy Protein Products


Meat foods Meat analogs and extenders Baked products Dairy-type foods Breakfast cereals and bars Infant formulations and baby foods Dietary and health foods Protein hydrolyzates (HVP) Confections pushed through protein enrichment and protein isolation, as well as through the application of mechanical, thermal, and chemical treatments, and selected combinations thereof. Nonetheless it is now recognized that limitations in the functional properties, including flavor, texture, and color, inhibit expanded utilization for the fabrication of food. Consequently, research interest in exploring various chemical and biochemical means for altering the functional properties of soy protein products is expanding. Indeed a recent report to the National Science Foundation on "Protein Resources and Technology" recommends the study of the "modification of the functionality of oilseeds and legume proteins by physical, chemical, and enzymatic methods to facilitate development of protein materials with wide versatility and acceptability in formulated foods" ( I ) . Soybean Proteins and Protein Products

In introducing the subject of chemical modification, we will describe briefly the proteins (2) and protein products of the soybean (3). Soybean Proteins. Protein products for food are derived from the cotyledonary tissue of the soybean seed. At the subcellular level (4) the proteins of the seed are distributed in cellular inclusions or protein bodies and in the surrounding cytoplasmic matrix (2). These proteins have often been grossly classified as storage globulins and biologically active proteins (Tables II and III). Although a number of the proteins have been separated in a reasonable state of purity (2), not one of the major storage globulins has been fully characterized down to the primary structure. In contrast, primary structures for two of the trypsin inhibitors, the Bowman-Birk and Kunitz inhibitors, have been elucidated through the notable efforts of Ikenaka and co-workers (5, 6). It now appears that at least seven of the soybean globulins have a multisubunit structure, and certain of these undergo association-dissociation reactions and sulfhydryl-disulfide interactions. While a review of the current state of knowledge about the structure and properties of the proteins of the

Feeney and Whitaker; Food Proteins Advances in Chemistry; American Chemical Society: Washington, DC, 1977.

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Table II. Major Storage Proteins of Defatted Soybean Flakes Ultracentrifuge Fraction

Approx. % H 0 Sol Protein

2S

18

7S

27

IIS 15S

34 6

2

Table III*

a-Conglyeinin(?) Others β-Conglycinin γ-Conglycinin Glycinin monomer Glycinin dimer Polymers (Glycinin tetramer, etc.)

Approx. Mol Wt 22,000 330,000(?) 180,000 180,000 360,000 600,000

Major Biologically Active Proteins of Defatted Soybean Flakes

Ultracentrifuge Fraction

Approx. % H 0 Sol Protein

2S

9

6S, 7S

6

2

Components

Components Trypsin inhibitors (multiple) Hemagglutinins (multiple) Lipoxygenase (iso-enzymes) Numerous enzyme systems: proteases, amylases, lipases, urease, etc.

Approx. Mol Wt 8,000 22,000 90,000100,000 100,000

Table IV. Potential Substrates for Chemical Modification Soy flours and grits—full-fat and defatted Soy protein concentrates Soy protein isolates Textured protein products a. spun fibers b. spun or extruded shreds c. extruded products d. compacted products Soy protein extracts or "milks" Soy "whey"



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soybean is not within the scope of this presentation, it is important to recognize that the incomplete and fragmentary nature of such knowledge makes the interpretation of chemical reactions difficult. Soy Protein Products. Over the years the variety of soy protein products available to the food processor has been expanding (3). In more recent years the introduction of such products has accelerated. The various classes of commercially available soy protein products are shown in Table IV. The first soybean protein ingredients made commercially available for food use included full-fat and defatted soy flours and grits (3, 7, 8). These products contain ca. 46-59% protein (Ν X 6.25) on a moisturefree basis and are available with various heat treatments for specific end-use. Soy protein concentrates and soy protein isolates were intro duced into the market about 15 years ago (3, 9, 10, 11). By definition soy protein concentrates must contain no less than 70% protein (Ν X 6.25) and isolates no less than 90% protein (Ν X 6.25), all on a moisure-free basis. In the past several years there has been much activity in the commercialization of textured soy protein products intended for the extension and replacement of meat. These textured products may be obtained through fiber spinning, shred formation, extrusion, or com paction (12, 13, 14, 15). In addition, soybean "milk" solids and the heterogeneous proteins in soybean "whey" might serve as useful sub strates in chemical modifications for food use. This short recitation of commercial products illustrates the type of crude protein fractions avail able for practical modification. Many useful functional properties have been ascribed to these new food proteins. Chemical Modification

The chemical modification of proteins has been reviewed recently in a monograph by Means and Feeney (16). Other useful reviews include those of Stark (17), Spande and Witkop (18), and Cohen (19). Feeney (20) has recently reviewed chemical changes in food proteins. This particular review should be consulted for additional references of both general and specific nature. The scope of this review is limited to those reactions with specific chemical reagents which result in the formation of new covalent bonds. It explicitly does not cover the many changes in protein structure caused by alteration of ionic, hydrogen, and hydrophobic bonding without con comitant establishment of new covalent bonds. In addition, the literature on this subject is reviewed in a very selective fashion simply to illustrate the types of chemical reactions studied and the nature and depth of such studies. Primary emphasis is placed upon investigations directed toward


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the modification of properties useful in food systems rather than those concerned solely with protein structure and biological properties (e.g., enzyme activity). Chemical modifications which have been suggested for altering the functional properties of soy proteins for food use are summarized in Table V . Since this information has been gleaned primarily from patent literature, it is not intended that this summary portray current commercial practice. Table V . Altered Functional Properties through Chemical Modification Reaction

Alkalies (pH > 10) sodium hydroxide, etc.

Acylation acetic anhydride succinic anhydride

Oxidation hydrogen peroxide (alkaline) chlorine peracid salts Reduction sulfite and related salts

Change in Properties

Increased dispersibility and solubility b. Increased resistance to aggregation (heat, etc.) c. Increased elasticity—better fiber formation a. b. c. d. e.

Improved solubility in acidic foods Increased solubility Lower viscosity Increased tolerance to Ca More resistance to aggregation 2+

Reduced viscosity

a. Reduced viscosity in water dispersion b. Increased viscosity in salt solution c. Increased resistance to aggregation

Examination of the literature on the chemical modification of proteins and protein-containing products derived from soybeans reveals that the major motivation for such studies was often the development of improved products for industrial rather than food or feed utilization (21, 22, 23, 24). Such research activity was at the heart of the Chemurgic movement begun in the early thirties. Hence it becomes understandable that the patent literature dealing with the chemical modification of soy protein products is much more extensive than the periodical literature. This, together with our imperfect understanding of the basic structure of the soy proteins, explains why many of the reactions cited in this



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review cannot be chronicled in detail as to reaction course or consequence but remain highly speculative in nature. This does, however, focus attention on the many areas which need clarification. It should be emphasized that chemically modified proteins intended for food use must be critically and extensively evaluated for their shortand long-term biological effects. Even chemical treatments not designed for modification of the protein products during processing, but applied for some processing advantage, must be studied at the molecular level to assess the biological implications of such treatment. Understandably, the design of biological experiments to evaluate these effects will be relevant to the intended food utilization. Alkalies and Acids. The older literature dealing with the treatment of soybean proteins with alkaline substances is quite extensive since these agents have often been used for protein extraction, solubilization, and property modification, including improved solubility, increased adhesive properties, and lower viscosity in dispersion andfiberformation (12, 21, 23, 24). The alkali treatment of soy protein for industrial use is done under conditions which are more severe (higher temperature and higher pH, such as possibly 50 °C at pH > 13) than those intended for food usage. More recently the alkaline treatment of soy proteins became a matter of concern with the finding by Woodard and Alvarez (25) that feeding of severely alkali-treated industrial soy protein to rats resulted in a cellular abnormality, cytomegaly, in the kidneys. Also, de Groot and Slump (26) demonstrated that severe alkaline treatment of a food-grade soy protein resulted in reduced nutritional value, disappearance of lysine, cystine, and serine, and the formation of lysinoalanine, LAL (27, 28). Recent work reported by de Groot and co-workers (29) indicates that the renal abnormality in rats is caused by free or peptide-bound LAL rather than protein-bound LAL. The relationship between biological activity and peptide structure has not been established. These workers also reported that the nephrotoxicity of LAL may be species-specific since they were unable to produce the cytomegalic response in mice, hamsters, dogs, monkeys, and quail at levels up to 1000 mg/kg diet. This question is expected to be resolved in the near future. In addition, more definitive descriptions of conditions used for alkaline treatments are needed. Lysinoalanine is formed by ^-elimination reaction of cystine-cysteine and serine with the formation of dehydroalanine and the subsequent addition of the e-amino group of lysine across the reactive C—C double bond (30). The formation of other amino acids such as ornithinoalanine (31), lanthionine (32), and ^-aminoalanine (33) by similar mechanism has been described. Gross et al. (34) have pointed out that lysinoalanine



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occurs in the antibiotics cynnamycin and duramycin. There is evidence that L A L occurs in food proteins and products which have not been alkali-treated (29, 35, 36), and hence other mechanisms for the formation of L A L must be operative. Feeney (20) has pointed out the importance of establishing the impact of alkaline treatment with each protein in question since such proteins may undergo significant changes under quite varied conditions. Acid hydrolyzates of soy protein products, either singly or in com bination with cereal grain proteins, are used extensively as flavoring agents in food (12, 22). These are commonly grouped in the familiar term "hydrolyzed vegetable protein." Milder acid treatment has been described for the deamidation of proteins, but this has not been exploited in altering the functional properties of soy proteins. Finley (37) has described a mild acid treatment of wheat gluten to increase its protein solubility in fruit-based acidic beverages. There is need to resolve whether such improvement results from deamidation of the glutamine and asparagine residues or from the concomitant cleavage of peptide bonds. Acylation. The acylation of soybean proteins with various acyl halides and anhydrides of low and high molecular weight was initially evaluated for its impact on properties of industrial value such as vis cosity in dispersion, adhesion, foaming, and detergency (22, 23, 24, 38). It is now evident that acylation with anhydrides ( such as acetic and succinic anhydrides) and with lactones (such as β-propiolactone) is being proposed (39) for improving the solubility of soy protein isolates at acidic pH, particularly for the preparation of coffee whiteners. More over, this chemical modification has been evaluated for altering the food-use properties of several milk proteins (40), egg protein (41 ), wheat protein (42), fish protein (43), and single-cell protein (44). Little attention has been given to the biological consequences of such acylation for food use. Creamer et al. (40) reported the result of growth and toxicity trials in rats and mice fed acetyl or succinyl casein and acetyl milk whey protein. These proteins had lower protein efficiency ratios than casein, and added L-lysine hydrochloride did not correct this deficiency. However, a trial with acetyl casein in mice showed no overt toxicity. These workers (40) concluded that none of the milk proteins as modified with anhydrides can be regarded as suitable for inclusion in acidic food products. It is obvious that a thorough biological evaluation is needed to assess whether acylated soy proteins are suitable for food use. Insofar as soy protein for food is concerned, no definitive study of the course of the acylation reaction has been made. Hoagland (45, 46), in a study of the acylation of β-casein, found that various acyl groups



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altered the calcium sensitivity of the protein and its ability to associate and to form aggregates. This work indicates that the predominant reaction is the acylation of the c-amino group of the lysine residues. A later study by Evans et al. (47) of the properties of the succinyl, maleyl, and glutaryl derivatives of ^-casein revealed that carboxyacylation is important in reducing casein—casein interactions and protein aggregation. These are basic changes of importance in modifying various novel food proteins, including soy protein, to fit the need in a diversity of food systems, both fluid and solid. Alkylation and Esterification. A number of alkylating, arylating, and related reagents have been used in studies concerned with the composition, structure, and conformation of various soybean proteins and protein fractions (2). Such studies are not within the scope of this review. In the modification of soy protein properties for food there is no evidence that either alkylation or esterification has been considered to any serious extent. McKinney and Uhing (48) examined the carboxymethylation of a commercial soy protein with sodium chloracetate in an alkaline medium. They found that the treated protein exhibited minimum solubility at a lower p H than did the untreated protein. In addition, the treated protein had increased resistance to reaction with formaldehyde, and, when exposed in the wet state, an increased resistance to putrefaction. These workers speculate as to the course of the reaction but give little evidence of the extent of reaction and reactive sites modified. Soy protein products have been treated with formaldehyde and a variety of other aldehydes and ketones, both simple and complex (21, 23, 24). These efforts were directed toward production of insolubilized protein for adhesives, films, coatings, polymers, etc. Soy protein products undergo the typical non-enzymatic browning reaction ( Maillard reaction ) in the presence of reducing sugars. The course of this reaction is similar to that of other proteins which have been studied in some detail. This subject has been reviewed recently by Feeney, Blankenhorn, and Dixon (49) as a special aspect of the carbonyl-amine reactions of proteins. Some years ago, Fraenkel-Conrat and Olcott reported on the esterification of proteins with low-molecular-weight alcohols (50). Included in this study were a number of food proteins including casein, gluten, gliadin, and egg albumin. The esterified proteins showed altered solubility behavior, as expected, from blocking of carboxyl groups. Although esterification has been applied to industrial soy proteins (21), it is doubtful, because of the sensitivity of the esters to hydrolysis, whether it would be of real value in altering food-use properties.



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Oxidation and Reduction. The patent literature concerned with the use of soy protein products for industrial purposes describes many oxidative treatments (21, 23, 24). The reagents most often cited include hydrogen peroxide, sodium peroxide, barium peroxide, and various oxidizing salts. Although this work gives little insight into the nature and extent of protein modification, it does indicate the issue of developing altered properties. Such oxidative treatments of soy protein have been applied mainly for color improvement or bleaching, increased solubility, and altered viscosity in alkaline dispersion. More recently, Johnson and Anderson (51) have described a process for preparing isolated oilseed proteins for food wherein the source material is extracted in an aqueous alkaline medium containing hydrogen peroxide. The process is said to be applicable to a variety of oilseed and grain products. It is claimed that the oxidative treatment results in improved protein yields. In another patent Melnychyn and Wolcott (52) describe a process for preparing an isolated soy protein with reduced dispersion viscosity and improved flavor. The reagents used in this process include oxidizing salts such as potassium bromate and iodate, sodium chlorate and chlorite, and ammonium persulfate, and also chlorine and bromine. In neither instance is the nature or extent of protein alteration defined. These modifications may include halogenation of aromatic residues in addition to oxidation of sensitive protein sites such as methylsulfhydryl, sulfhydryl, and disulfide groups. One of the most important applications of hydrogen peroxide in the food industry is reported to be preservation (53). This simple oxidant has been recognized as an alternative antimicrobial agent in milk systems (54). Such recognition has prompted a number of studies of the alteration of milk proteins by hydrogen peroxide (55). Hydrogen peroxide has also been evaluated in the production of a peanut protein concentrate (56) and for the detoxification of rapeseed flour for food use (57). The course of the reaction of hydrogen peroxide and several other oxidizing reagents with proteins has been reviewed by Means and Feeney (16). The vulnerable protein sites include those of cysteine and methionine, and in certain instances cystine, tryptophan, and tyrosine. These reactions are of interest to the protein biochemist concerned with protein structure and bioactivity, yet the fundamental concern here is whether oxidation results in beneficial alteration of properties for food and whether such treatment results in diminished nutritive value. In recent years, several reports have dealt with the decreased nutritional value of oxidized food proteins (53, 57, 58, 59). Although oxidation per se of the sulfur amino acids is a factor in reduced nutritive



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quality, Cuq et al. (58, 59) have demonstrated that oxidation of the intact protein causes a sharp reduction in the release of methionine by in vitro enzymatic digestion (60). This may be the answer to the enigma of the biological availability of methionine sulfoxide in intact proteins. Obviously, further work is needed to resolve this matter. It has now been recognized that protein oxidation may arise through reaction with lipid hydroperoxides (60). This is of practical significance with the increasing production of processed composite foods and their extended storage in reaching the ultimate consumer. The nutritional significance of methionine oxidation in casein systems by autoxidizing lipids was described by Tannenbaum et al. (61). Autoxidizing lipids have been implicated in the generation of undesirable flavors in soy protein products (12, 62). The role of oxidizing indigenous and added lipids deserves further study concerning their impact on the flavor and, more importantly, the nutritional quality of food ingredients and food products. Sodium sulfite and related sulfiting substances have been favored reagents in the extraction and preparation of protein products from defatted soybean meal for industrial, feed, and food purposes (21, 23, 24). The use of sodium sulfite or sulfur dioxide in the production of soy protein isolates has been described in a number of patents (3, 23, 63). Although not always explicitly stated, the purpose of such use has been to improve the extractability of the protein and to inhibit the aggregation of the isolated protein. Such treatment results in proteins with improved solubility and reduced viscosity. The use of sulfite also affords the beneficial effect of retarding the growth of micro-organisms during the wet processing of the protein. The chemistry of the reaction of sulfites with proteins has recently been reviewed by Means and Feeney (16). It is presumed that the described course of the reaction applies to soy proteins, at least in a general sense. Because of the long history of the use of sulfur dioxide and sulfites in food and beverage processing, and in food preservation, the literature dealing with their use and food safety is quite extensive. Much of this literature has been reviewed in a U.S. Food and Drug Administration ( F D A ) re-examination of the Generally Recognized As Safe (GRAS) status of sulfiting agents for food (64, 65). Although this re-examination has not been completed, these agents ( sodium sulfite, sodium bisulfite, sodium metabisulfite, potassium bisulfite, potassium metabisulfite, and alkali sulfites ) continue to be recognized as safe by the F D A . Earlier it had been suggested that bound sulfur dioxide, such as that reacted with protein, may be more toxic than the free sulfites as demonstrated by significantly decreased growth rate in rats (66). Gibson



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and Strong (67) repeated this work and found that sulfite-treated casein produced growth rates in rats equal to that of untreated casein. Although evidence to date indicates that proteins treated with sulfiting agents are safe for use in food, further information relating conditions from laboratory studies to conditions used in commercial practices is desirable. The thiols, mercaptoethanol and diethiothreitol, have been used extensively for the reductive cleavage of disulfide bonds and for the maintenance of a reductive environment in the isolation and characterization of specific soybean proteins (2). However, these reagents have not been used for the preparation of protein products for food. The odor and flavor of the low-molecular-weight thiol compounds are not compatible with usage in a broad range of food items, yet these substances contribute to the desirable odor and flavor of selected foods. Other Reactions. Various soy protein products have been treated with numerous organic reagents in efforts to develop properties useful in adhesives, plastics, films, coatings, textile fibers, and the like (21, 23, 24). These purposefully modified proteins have not been recommended for food use. On the other hand, it has now been recognized that the treatment of soybeans or soybean proteins with chemical substances in processing for component fractionation or isolation may result in the unrecognized production of toxic reaction products. A classic and historic example is the defatting of soybeans with trichloroethylene (TCE) to produce defatted soybean meal for animal feeding. During the late 1940s and early 50s it was determined that the feeding of TCE-extracted soybean oil meal (TESOM) resulted in many cases of fatal aplastic anemia in cattle (68). After much investigation it was concluded that the toxicity resulted from reaction of the protein with T C E to produce protein-bound S-dichlorovinylcysteine (69). Further, the corresponding synthetic amino acid was shown to produce the typical syndrome of aplastic anemia when orally administered to experimental animals. This experience underscores the need to examine critically the biochemical and biological consequences of both intentional and incidental protein modification caused by exposure to chemical reagents. In addition, the T C E toxicity problem indicates that specific reagent activity with proteins must be considered with regard to environmental conditions including concentration, temperature, moisture, p H , time, etc. An enigma in the T E S O M problem was that all TCE-extracted soybean meals did not cause aplastic anemia. This was found to be related to temperature during fat extraction. Fortunately, TCE-extracted meals were prepared for animal feeds, and apparently in recent years there have not been any proven cases of toxicities to humans from the purposeful chemical modification of food proteins.


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Functional Properties of Soy Proteins

Any discussion of the modification of the functional properties of soy proteins for food use is incomplete without some comment on the nature and measurement of such properties. Various practical functional properties useful in processed food production have been ascribed to soy protein products (12, 70, 71, 72). These properties have become evident in the evaluation of soy proteins for the production of food products having recognized acceptance characteristics. Traditional knowledge of a proteins physical and chemical properties is much less significant in innovative food items. The properties ascribed to soy protein products include: (a) emulsion formation and stabilization, (b) fat absorption, (c) water absorption and retention, (d) viscosity generation, (e) gellation, (f) chunk, shred, fiber, and lamininate formation, (g) film formation, (h) dough formation, (i) adhesion and cohesion, (j) elasticity, (k) aeration, and (1) foam formation and stabilization (70, 71, 72). The increasing effort to evaluate the food potential of a diversity of novel proteins has focused attention on methods to evaluate their potential utility in food fabrication. This attention has revealed that simple bench-top methods have little relevancy to complex food systems. Pour-El, in a review of the measurement of the functional properties of soy protein products (73), has concluded that "what is most lacking is a set of standardized methods which have been tested with numerous products and correlated with actual food tests." Viewing the broad problem in a more fundamental sense makes it obvious that there is a serious lack of knowledge concerning the relation of basic protein structure to functional behavior. Such understanding would provide a rational basis for developing new proteins with predetermined specific properties for food use. Conclusion

A review of the patent and periodical literature reveals that the intentional chemical modification of soy protein products for food use has received little attention. Such work as has been described is concerned with crude protein-containing fractions and heterogeneous protein mixtures. The full nature and extent of these chemical reactions have not been defined. In spite of the lack of definitive chemical modification studies, there is evidence of the beneficial alteration of gross properties related to potential food use. Thus there exists a challenge in modifying soy proteins and other novel proteins through chemical reactions to make them more suitable for the extension and replacement of existing food proteins in processed foods and for the fabrication of new foods. Each modified protein in-


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tended for food use must be critically evaluated for short- and long-term biological effects related to the fundamental matters of food value and food safety. This need may be considered a deterent to the exploration of the value of chemical modification of proteins, yet such modification may play a significant role in achieving an extensive food utilization of novel proteins in the long years ahead.

Literature Cited 1. Milner, M. (Coordinator), "Protein Resources and Technology, Status and Research Needs," Report to the National Science Foundation, Oct. 6, 1975. 2. Wolf, W., in "Soybeans: Chemistry and Technoloy," Vol. 2 of "Proteins," A. K. Smith, S. J. Circle, Eds., Avi, Westport, Conn., 1972. 3. Circle, S., Smith, Α., in "Soybeans: Chemistry and Technology," Vol. 1 of "Proteins," A. K. Smith, S. J. Circle, Eds., Avi, Westport, Conn., 1972. 4. Wolf, W., Baker, F., Cereal Sci. Today (1972) 17, 125. 5. Odani, S., Ikenaka, T.,J.Biochem. (1973) 74, 697. 6. Koide, T., Ikenaka, T., Eur.J.Biochem. (1973) 32, 417. 7. Horan, F., "Defatted and Full Fat Soy Flours by Conventional Processes," in "Processing of International Conference on Soybean Foods," Publica tion ARS-71-35, USDA, Wash., D. C., 1967. 8. Meyer, E., "Soybean Flours and Grits," Proc. SOS/70 Int. Congr. Foo Sci. Technol., 3rd, 1971. 9. Meyer, E., J. Am. Oil Chem. Soc. (1971) 48, 484. 10. Meyer, E., "Soya Protein Isolates for Food," in "Protein as Human Food," R. A. Lawrie, Ed., Butterworths, London, England, 1970. 11. Meyer, E., Williams, L. D., "Soy Protein Concentrates and Isolates," in "Proceedings World Soybean Research Conference," Univ. of Illinois, Champaign,Ill.,1975. 12. Smith, Α., Circle, S., "Protein Products as Food Ingredients," in "Soybeans: Chemistry and Technology," Vol. 1 of "Proteins," A. K. Smith, S. J. Circle, Eds., Avi, Westport, Conn., 1972. 13. Horan, F., in "New Protein Foods," Vol. 1A of "Technology," A. Altschul, Ed., Academic, New York, N.Y., 1974. 14. Ashton, M., Burke, C., Holmes, Α., in "Scientific and Technical Surveys," No. 62, British Food Mfg. Inc. Research Assoc., Letherhead, Surrey, England, 1970. 15. Burke, C., "Textured Vegetable Proteins, II," "Survey of U.K. and U.S. Patent Literature," Scientific and Technical Surveys, No. 63, British Food Mfg. Ind. Research Assoc., Leatherhead, Surrey, England, 1971. 16. Means, G., Feeney, R., "Chemical Modification of Proteins," Holden-Day, San Francisco, 1971. 17. Stark, G., Adv. Protein Chem. (1970) 24, 261. 18. Spande, T., Witkop, B., Degani, Y., Patchornik, Α., Adv. Protein Chem. (1970) 24, 97. 19. Cohen, L., Annu. Rev. Biochem. (1968) 37, 695. 20. Feeney, R., in "Proteins for Human Consumption," C. E. Bodwell, Ed., Avi, Westport, Conn., in preparation. 21. Circle, S., in "SoybeansandSoybean Products," Vol. I, K. S. Markley, Ed., Interscience, New York, 1950. 22. Burnett, R., in "Soybeans and Soybean Products," Vol. II, K. S. Markley, Ed., Interscience, New York, 1951. 23. Burnett, R., in "Soybeans and Soybean Products," Vol. II, K. S. Markley, Ed., Interscience, New York, 1951. Feeney and Whitaker; Food Proteins Advances in Chemistry; American Chemical Society: Washington, DC, 1977.


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